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POwhat log value to use for Kullback leibler divergence implementation?
 

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  1. POwhat log value to use for Kullback leibler divergence implementation?
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    <p>I have done a method to implement the Kullback-leibler divergence in java. I have used the log with base 2 value and i am not sure whether i have used it right or i should used log base 10 value. I am using this method to measure the divergence between two text units(each of different length). </p> <p>My problem is i don't get the desired divergence measure . </p> <p>for example for two text units namely => "Free Ringtones" and the second one "Free Ringtones for your Mobile Phone from PremieRingtones.com" </p> <p>I should get a divergence of 0.25(as of my project references) but i get a divergence of 2.0 if i use log base2 and 1.38 for log base10. </p> <p>Also i am unaware of what value to substitute instead of zero value for demnominator.Plz help in giving clear explaination with some examples if possible and even some links to where i can get details.</p> <p>This is My code snippet: </p> <pre><code>public Double calculateKLD(List&lt;String&gt; values,List&lt;String&gt; value2) { Map&lt;String, Integer&gt; map = new HashMap&lt;String, Integer&gt;(); Map&lt;String, Integer&gt; map2 = new HashMap&lt;String, Integer&gt;(); for (String sequence : values) { if (!map.containsKey(sequence)) { map.put(sequence, 0); } map.put(sequence, map.get(sequence) + 1); } for (String sequence : value2) { if (!map2.containsKey(sequence)) { map2.put(sequence, 0); } map2.put(sequence, map2.get(sequence) + 1); } Double result = 0.0; Double frequency2=0.0; for (String sequence : map.keySet()) { Double frequency1 = (double) map.get(sequence) / values.size(); System.out.println("Freuency1 "+frequency1.toString()); if(map2.containsKey(sequence)) { frequency2 = (double) map2.get(sequence) / value2.size(); } result += frequency1 * (Math.log(frequency1/frequency2) / Math.log(2)); } return result/2.4; } </code></pre> <p>My Input is like this </p> <p><strong>First text unit</strong></p> <pre><code> list.add("Free");list.add("Ringtones"); </code></pre> <p><strong>Second text unit</strong></p> <pre><code> list2.add("Free");list2.add("Ringtones");list2.add("for");list2.add("your");list2.add("Mobiile");list2.add("Phone");list2.add("from");list2.add("PremieRingtones.com"); </code></pre> <p>Calling function </p> <pre><code> calculateKLD(list, list2) </code></pre>
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    1. USNaveen
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    1. COUsing different logarithms will yield proportional values. With log2, we say divergence is expressed in **bits**, with natural log in **nats** and with log10, well, I don't know about any terminology, but you usually end with **decibels** after multiplying by 10. They are bona fide units, with a constant conversion factor between them, like meters and miles, pounds and metric tons, etc.
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      1. POwhat log value to use for Kullback leibler divergence implementation?
      1. USAlexandre C.
    2. COwell if you use log256, you'll get 0.25. It looks like your computation is correct. when i manually calculate it, i get 2.0. If you switch it around and do D_KL(Q||P), I get -0.5.
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      1. POwhat log value to use for Kullback leibler divergence implementation?
      1. USealdent
 

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